Catalyst and process for producing liquefied petroleum gas

ABSTRACT

A catalyst for producing a liquefied petroleum gas according to the present invention comprises a Pd- and/or Pt-based catalyst component and a USY-type zeolite. By using the catalyst, a hydrocarbon containing propane or butane as a main component, i.e. a liquefied petroleum gas, can be produced with high activity, high selectivity and high yield from at least one of methanol and dimethyl ether.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.11/465,720, filed on Aug. 18, 2006, which claims priority to JapanesePatent Application No. 2005-321,864, filed Nov. 7, 2005, which arehereby incorporated by reference in there entirety.

TECHNICAL FIELD

This invention relates to a catalyst for producing a liquefied petroleumgas containing propane or butane as a main component by reacting atleast one selected from the group consisting of methanol and dimethylether with hydrogen. This invention also relates to a process forproducing a liquefied petroleum gas using the catalyst.

Furthermore, this invention relates to a process for producing aliquefied petroleum gas containing propane or butane as a main componentfrom a synthesis gas, via methanol and/or dimethyl ether. This inventionalso relates to a process for producing a liquefied petroleum gascontaining propane or butane as a main component from acarbon-containing starting material such as a natural gas, via methanoland/or dimethyl ether.

BACKGROUND OF THE INVENTION

Liquefied petroleum gas (LPG) is a liquefied petroleum-based ornatural-gas-based hydrocarbon which is gaseous at an ambient temperatureunder an atmospheric pressure by compression while optionally cooling,and the main component of it is propane or butane. LPG is advantageouslytransportable because it can be stored or transported in a liquid form.Thus, in contrast with a natural gas that requires a pipeline forsupply, it has a characteristic that it can be filled in a container tobe supplied to any place. For that reason, LPG comprising propane as amain component, i.e. propane gas, has been widely used as a fuel forhousehold and business use. At present, propane gas is supplied to about25 million households (more than 50% of the total households) in Japan.In addition to household and business use, LPG is used as a fuel for aportable product such as a portable gas burner and a disposable lighter(mainly, butane gas), an industrial fuel and an automobile fuel.

Conventionally, LPG has been produced by 1) collection from a wetnatural gas, 2) collection from a stabilization (vapor-pressureregulating) process of crude petroleum, 3) separation and extraction ofa product in, for example, a petroleum refining process, or the like.

LPG, in particular propane gas used as a household/business fuel, can beexpected to be in great demand in the future. Thus, it may be veryuseful to establish an industrially practicable and new process forproducing LPG.

As a process for producing LPG, Japanese Patent Laid-open PublicationNo. 61-23688 discloses that a synthesis gas consisting of hydrogen andcarbon monoxide is reacted in the presence of a mixed catalyst obtainedby physically mixing a methanol synthesis catalyst, specifically aCuO—ZnO—Al₂O₃ catalyst or a Pd/SiO₂ catalyst, with a methanol conversioncatalyst composed of a zeolite having an average pore size of about 10 Å(1 nm) or more, specifically a Y-type zeolite, to give a liquefiedpetroleum gas or a mixture of hydrocarbons similar in composition toLPG.

However, the above-mentioned process does not always give a sufficientlyhigh activity (a conversion of carbon monoxide), a sufficiently highyield of a hydrocarbon, and a sufficiently high yield of propane andbutane. A yield of hydrocarbon is at most 36.0%, while a yield ofpropane and butane is about 26%. In another case, a yield of hydrocarbonis 35.7%, while a yield of propane and butane is about 27%.

Furthermore, a product obtained by the above-mentioned process may nothave a sufficiently low carbon dioxide content. When a yield ofhydrocarbon is at its highest, that is 36.0%, a yield of carbon dioxideis 33.9%. When a yield of hydrocarbon is 35.7%, a yield of carbondioxide is 30.7%. Carbon dioxide is less useful and is hard to bereused, and therefore, it is economically undesirable to yield a largeamount of carbon dioxide as a by-product.

As a process for producing LPG, “Selective Synthesis of LPG fromSynthesis Gas”, Kaoru Fujimoto et al., Bull. Chem. Soc. Jpn., 58, p.3059-3060 (1985) discloses that, using a hybrid catalyst consisting of amethanol synthesis catalyst such as a 4 wt % Pd/SiO₂, a Cu—Zn—Al mixedoxide {Cu:Zn:Al=40:23:37 (atomic ratio)} or a Cu-based low-pressuremethanol synthesis catalyst (Trade name: BASF S3-85) and a high-silicaY-type zeolite with SiO₂/Al₂O₃=7.6 treated with steam at 450° C. for 1hour, C2 to C4 paraffins can be produced in a selectivity of 69 to 85%via methanol and dimethyl ether from a synthesis gas. However, as is inthe process described in the above-mentioned Japanese Patent Laid-openPublication No. 61-23688, this process does not always give asufficiently high activity (a conversion of carbon monoxide) and asufficiently high yield of a hydrocarbon, and the obtained product maynot have a sufficiently low carbon dioxide content.

On the other hand, “Methanol/Dimethyl Ether Conversion on ZeoliteCatalysts for Indirect Synthesis of LPG from Natural Gas”, Yingjie Jinet al., Dai 92 Kai Shokubai Touronkai TouronkaiA Yokousyuu, (thesummaries of the 92th Catalysis Society of Japan (CatSJ) Meeting,Meeting-A), p. 322, Sep. 18, 2003 discloses a process for producing LPG,using at least one selected from the group consisting of methanol anddimethyl ether as a starting material. Specifically, a starting gas,whose composition is methanol:H₂:N₂=1:1:1, was passed through thetwo-layered catalyst layer consisting of ZSM-5 as the former layer andPt-C as the latter layer (ZSM-5/Pt-C Series) or a mixed catalyst layerconsisting of ZSM-5 and Pt-C (ZSM-5/Pt-C Pellet-mixture), under aslightly increased pressure, at a reaction temperature of 603 K (330°C.) and at a methanol-based LHSV of 20 h⁻¹, whereby carrying out an LPGproduction reaction.

However, the above-mentioned process may not give a sufficiently highconversion of methanol to propane and butane. When using a ZSM-5/Pt-CSeries as a catalyst layer, a conversion of methanol to a hydrocarbon is64.0% on the basis of carbon, while a conversion of methanol to propaneand butane is about 38.7% on the basis of carbon. When using aZSM-5/Pt-C Pellet-mixture as a catalyst layer, the result is even worse;specifically, a conversion of methanol to a hydrocarbon is 20.6% on thebasis of carbon, while a conversion of methanol to propane and butane isabout 10.8% on the basis of carbon.

Furthermore, when using a ZSM-5/Pt-C Series as a catalyst layer, thedeterioration with time of the catalyst may be generally significant andthe catalyst life may not be sufficiently long. Generally, when anolefin is produced from methanol and/or dimethyl ether using a zeoliteas a catalyst, the zeolite catalyst is apt to be deteriorated due tocoking.

SUMMARY OF THE INVENTION

An objective of this invention is to provide a catalyst for producing ahydrocarbon containing propane or butane as a main component, i.e. aliquefied petroleum gas (LPG), with high activity, high selectivity andhigh yield, from at least one selected from the group consisting ofmethanol and dimethyl ether.

Another objective of this invention is to provide a process foreconomically producing a liquefied petroleum gas (LPG) with a highyield, from at least one selected from the group consisting of methanoland dimethyl ether, using the above catalyst.

The present invention provides a catalyst for producing a liquefiedpetroleum gas, which is used for producing a liquefied petroleum gascontaining propane or butane as a main component by reacting at leastone selected from the group consisting of methanol and dimethyl etherwith hydrogen, comprising a Pd- and/or Pt-based catalyst component inwhich Pd and/or Pt is supported on a support; and a USY-type zeolite.

The present invention also provides a process for producing a liquefiedpetroleum gas, comprising a step of:

reacting at least one selected from the group consisting of methanol anddimethyl ether with hydrogen in the presence of the above catalyst,whereby producing a liquefied petroleum gas containing propane or butaneas a main component.

Furthermore, the present invention provides a process for producing aliquefied petroleum gas, comprising:

(1) a step of producing methanol wherein a synthesis gas is passedthrough a catalyst layer comprising a methanol synthesis catalyst,whereby producing a reactant gas containing methanol and hydrogen; and

(2) a step of producing a liquefied petroleum gas wherein the reactantgas produced in the step of producing methanol is passed through acatalyst layer comprising the above catalyst, whereby producing aliquefied petroleum gas containing propane or butane as a maincomponent.

And, the present invention also provides a process for producing aliquefied petroleum gas, comprising:

(1) a step of producing dimethyl ether wherein a synthesis gas is passedthrough a catalyst layer comprising a methanol synthesis catalyst and amethanol dehydration catalyst, whereby producing a reactant gascontaining dimethyl ether and hydrogen; and

(2) a step of producing a liquefied petroleum gas wherein the reactantgas produced in the step of producing dimethyl ether is passed through acatalyst layer comprising the above catalyst, whereby producing aliquefied petroleum gas containing propane or butane as a maincomponent.

Furthermore, the present invention provides a process for producing aliquefied petroleum gas, comprising:

(1) a step of producing a synthesis gas from a carbon-containingstarting material and at least one selected from the group consisting ofH₂O, O₂ and CO₂;

(2) a step of producing methanol wherein the synthesis gas is passedthrough a catalyst layer comprising a methanol synthesis catalyst,whereby producing a reactant gas containing methanol and hydrogen; and

(3) a step of producing a liquefied petroleum gas wherein the reactantgas produced in the step of producing methanol is passed through acatalyst layer comprising the above catalyst, whereby producing aliquefied petroleum gas containing propane or butane as a maincomponent.

And, the present invention also provides a process for producing aliquefied petroleum gas, comprising:

(1) a step of producing a synthesis gas from a carbon-containingstarting material and at least one selected from the group consisting ofH₂O, O₂ and CO₂;

(2) a step of producing dimethyl ether wherein the synthesis gas ispassed through a catalyst layer comprising a methanol synthesis catalystand a methanol dehydration catalyst, whereby producing a reactant gascontaining dimethyl ether and hydrogen; and

(3) a step of producing a liquefied petroleum gas wherein the reactantgas produced in the step of producing dimethyl ether is passed through acatalyst layer comprising the above catalyst, whereby producing aliquefied petroleum gas containing propane or butane as a maincomponent.

Herein, the term “synthesis gas” refers to a mixed gas comprisinghydrogen and carbon monoxide, and is not limited to a mixed gasconsisting of hydrogen and carbon monoxide. A synthesis gas maycomprise, for example, carbon dioxide, water, methane, ethane, ethyleneand the like. A synthesis gas produced by reforming a natural gasgenerally contains, in addition to hydrogen and carbon monoxide, carbondioxide and water vapor. A synthesis gas may be a coal gas produced bycoal gasification or a water gas produced from a coal coke.

A catalyst for producing a liquefied petroleum gas according to thisinvention comprises a Pd- and/or Pt-based catalyst component in which Pdand/or Pt is supported on a support, and a USY-type zeolite. Examples ofa Pd- and/or Pt-based catalyst component include Pd/SiO₂ and Pt/SiO₂. Byreacting at least one selected from the group consisting of methanol anddimethyl ether with hydrogen in the presence of the catalyst accordingto this invention, a hydrocarbon containing propane or butane as a maincomponent, i.e. a liquefied petroleum gas (LPG) can be produced withhigh activity, high selectivity and high yield. Particularly, accordingto this invention, the decomposition of methanol and/or dimethyl etherto CO and CO₂ may be inhibited and therefore, the production amount ofcarbon monoxide and carbon dioxide as by-products may be significantlyreduced, while keeping the conversion of methanol and/or dimethyl etherhigh.

In this invention, LPG containing propane or butane as a main componentmay be produced from at least one selected from the group consisting ofmethanol and dimethyl ether, and hydrogen, in accordance with thefollowing formula (I).

In this invention, methanol is dehydrated to generate a carbene (H₂C:)by a concerted catalysis of an acidic site and a basic site, which areat a spatial field inside a pore in a USY-type zeolite. And then, thecarbene is polymerized to form an olefin containing propylene or buteneas a main component. More specifically, it may be thought that ethyleneis formed as a dimer; propylene is formed as a trimer or a reactionproduct with ethylene; and butylene is formed as a tetramer, a reactionproduct with propylene or a product of dimerization of ethylene.

In the olefin formation process, there would occur other reactions suchas formation of dimethyl ether by dehydration-dimerization of methanoland formation of methanol by hydration of dimethyl ether.

And then, the formed olefin is hydrogenated mainly by the catalysis of aPd- and/or Pt-based catalyst component, to form a paraffin containingpropane or butane as a main component, i.e. LPG.

According to this invention, for example, a hydrocarbon with the totalcontent of propane and butane of 55% or more, specifically 60% or moreon the basis of carbon can be produced with high activity and highselectivity, specifically a conversion of methanol and/or dimethyl etherto a hydrocarbon of 90% or more, more specifically 95% or more.

According to this invention, LPG can be produced with a conversion ofmethanol and/or dimethyl ether to propane and butane of 55% or higher,specifically 60% or higher on the basis of carbon. Furthermore,according to this invention, a conversion of methanol and/or dimethylether to carbon monoxide and carbon dioxide can be reduced to 6% orless, particularly 4% or less on the basis of carbon.

When reacting at least one selected from the group consisting ofmethanol and dimethyl ether with hydrogen to produce a liquefiedpetroleum gas, a product generally includes, in addition to propane andbutane as main components, other hydrocarbons such as ethane, methane,pentane and hexane. These hydrocarbons other than propane and butane areby-products in an LPG production reaction, but they are more useful thancarbon monoxide and carbon dioxide. The hydrocarbons other than propaneand butane can be used as, for example, a calorie adjustor for town gas,a chemical raw material, a gasoline fuel and the like. Moreover,methanol, which is used as a starting material in this invention, isindustrially produced on a large scale from a synthesis gas, and thehydrocarbons other than propane and butane can be used as a startingmaterial for producing the synthesis gas. It is economicallyadvantageous to yield a small amount of carbon monoxide and carbondioxide as a by-product.

In the synthesis reaction of an olefin from methanol and/or dimethylether, a zeolite catalyst is apt to be deteriorated due to coking, andtherefore, may not have a sufficiently long catalyst life. In contrast,according to the process for producing LPG of this invention, even whenusing a zeolite-containing catalyst, deterioration of a zeolite due tocoking can be prevented and thus LPG can be stably produced for a longperiod with reducing a catalyst cost.

Furthermore, in a hydrogenation reaction of an olefin, carbon monoxideand carbon dioxide may act as a catalyst poisoning component, and theformation of methane by hydrogenation may occur. Therefore, a gascontaining carbon monoxide and/or carbon dioxide is not preferable as astarting gas (a gas fed into a reactor). In contrast, in the process forproducing LPG of this invention, the presence of carbon monoxide and/orcarbon dioxide in a starting gas has no effect on LPG production.

Methanol, which is a reaction raw material, is industrially produced ona large scale from a synthesis gas, and the product of the methanolsynthesis reaction generally contains carbon monoxide, which is anunreacted starting material, and carbon dioxide, which is a by-product.Dimethyl ether can be also produced from a synthesis gas, and theproduct of the dimethyl ether synthesis reaction also generally containscarbon monoxide and/or carbon dioxide. When constructing a processcomprising the step of producing methanol and/or dimethyl ether from asynthesis gas and the following step of producing LPG from methanoland/or dimethyl ether, employing the process for producing LPG of thisinvention may be economically advantageous, because it is not necessaryto purify a product after methanol and/or dimethyl ether synthesisreaction, and thus the product can be used as a starting material forproducing LPG without any treatment.

As described above, according to this invention, a hydrocarboncontaining propane or butane as a main component, i.e. a liquefiedpetroleum gas (LPG), can be economically produced with a relativelyhigher yield from at least one selected from the group consisting ofmethanol and dimethyl ether, or from a synthesis gas.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a process flow diagram showing a main configuration in anexample of an LPG producing apparatus suitable for conducting theprocess for LPG production according to this invention.

DESCRIPTION OF THE MAIN SYMBOLS

-   -   11: a reactor    -   11 a: a catalyst layer containing a catalyst for producing a        liquefied petroleum gas    -   12, 13: lines.

DETAILED DESCRIPTION OF THE EMBODIMENTS 1. Catalyst for Producing aLiquefied Petroleum Gas According to the Present Invention

A catalyst for producing a liquefied petroleum gas according to thepresent invention comprises a Pd- and/or Pt-based catalyst component inwhich Pd and/or Pt is supported on a support, and a USY-type zeolite. Acatalyst for producing a liquefied petroleum gas of this invention cancomprise other additive components as long as its intended effect wouldnot be impaired.

A ratio of the Pd- and/or Pt-based catalyst component to the USY-typezeolite (Pd- and/or Pt-based catalyst component/USY-type zeolite; byweight) is preferably 0.1 or more, more preferably 0.3 or more. Byadjusting a ratio of the Pd- and/or Pt-based catalyst component to theUSY-type zeolite (Pd- and/or Pt-based catalyst component/USY-typezeolite; by weight) to 0.1 or more, a higher yield of propane and butanecan be achieved.

A ratio of the Pd- and/or Pt-based catalyst component to the USY-typezeolite (Pd- and/or Pt-based catalyst component/USY-type zeolite; byweight) is preferably 1.5 or less, more preferably 1.2 or less,particularly preferably 0.8 or less. By adjusting a ratio of the Pd-and/or Pt-based catalyst component to the USY-type zeolite (Pd- and/orPt-based catalyst component/USY-type zeolite; by weight) to 1.5 or less,a higher yield of propane and butane can be achieved, and furthermorethe production amount of carbon monoxide, carbon dioxide and methane asby-products can be more sufficiently reduced. By adjusting a ratio ofthe Pd- and/or Pt-based catalyst component to the USY-type zeolite (Pd-and/or Pt-based catalyst component/USY-type zeolite; by weight) to 0.8or less, a further higher yield of propane and butane can be achieved,and the production amount of heavy hydrocarbons (C5 or more) asby-products can be more sufficiently reduced.

By adjusting a ratio of the Pd- and/or Pt-based catalyst component tothe USY-type zeolite within the above range, propane and/or butane canbe produced with a higher selectivity and a higher yield.

A ratio of the Pd- and/or Pt-based catalyst component to the USY-typezeolite is not limited to the above range, and can be appropriatelydetermined, depending on the amount of Pd and/or Pt in the Pd- and/orPt-based catalyst component, and the like.

(Pd- and/or Pt-Based Catalyst Component)

A Pd- and/or Pt-based catalyst component is Pd and/or Pt supported on asupport. In the light of catalytic activity, Pd and/or Pt is preferablysupported on a support in a highly dispersed manner.

Pd and/or Pt may not be necessarily contained as a metal, but can becontained in the form of an oxide, a nitrate, a chloride or the like. Insuch a case, for achieving higher catalytic activity, the catalyst canbe preferably subjected to, for example, reduction by hydrogen beforethe reaction, to convert Pd and/or Pt in the Pd- and/or Pt-basedcatalyst component into metallic palladium and/or metallic platinum.

The amount of supported Pd and/or Pt in a Pd- and/or Pt-based catalystcomponent is preferably 0.1 wt % or more, more preferably 0.3 wt % ormore. In the light of dispersibility and economical efficiency, theamount of supported Pd and/or Pt in a Pd- and/or Pt-based catalystcomponent is preferably 5 wt % or less, more preferably 3 wt % or less.By adjusting the amount of supported Pd and/or Pt in a Pd- and/orPt-based catalyst component within the above range, propane and/orbutane can be produced with a higher conversion, a higher selectivityand a higher yield.

A support for Pd- and/or Pt-based catalyst component may be selectedfrom known supports without limitation. Examples of a support includesilica (silicon dioxide), alumina, silica-alumina, carbon (activatedcharcoal); and oxides of zirconium, titanium, cerium, lanthanum, iron orthe like, and composite oxides containing two or more types of thesemetals, and composite oxides containing one or more types of thesemetals and one or more types of other metals. Such supports may be usedalone or in combination of two or more.

Among others, a preferable support for Pd- and/or Pt-based catalystcomponent is silica. By using silica as a support, propane and/or butanecan be produced with a higher selectivity and a higher yield withoutproducing carbon dioxide as a by-product.

A silica support preferably has a specific surface area of 450 m²/g ormore, more preferably 500 m²/g or more. By using a silica support havinga specific surface area within the above range, higher catalyticactivity can be achieved and propane and/or butane can be produced witha higher conversion and a higher yield.

The upper limit of a specific surface area of a silica support is notparticularly restricted, but is generally about 1000 m²/g.

A specific surface area of silica can be determined, for example, by aBET method using N₂ as an adsorption gas and a fully automatic measuringapparatus for specific surface area and pore distribution (e.g.,ASAP2010, Shimadzu Corporation).

In this invention, a Pd- and/or Pt-based catalyst component may be asilica support on which other components, in addition to Pd and Pt, aresupported as long as the desired effects of the catalyst are maintained.

(USY-Type Zeolite)

A USY-type zeolite used in this invention may be selected from USY-typezeolites containing a metal such as alkali metals, alkaline earth metalsand transition metals; USY-type zeolites ion-exchanged with these metalsor the like; and USY-type zeolites on which these metals or the like aresupported. But a preferable USY-type zeolite is a proton-type zeolite.By using a proton-type USY-type zeolite having a suitable acid strengthand a suitable acidity (acid concentration), higher catalytic activitycan be achieved, and propane and/or butane can be produced with a higherconversion and a higher selectivity.

A SiO₂/Al₂O₃ ratio of a USY-type zeolite is more preferably 5 or more,particularly preferably 15 or more. By using a USY-type zeolite with aSiO₂/Al₂O₃ ratio of 5 or more, particularly preferably 15 or more, theproduction amount of carbon monoxide and carbon dioxide as by-productscan be more sufficiently reduced, and a higher selectivity of propaneand butane can be achieved.

And, a SiO₂/Al₂O₃ ratio of a USY-type zeolite is more preferably 50 orless, particularly preferably 40 or less, further preferably 25 or less.By using a USY-type zeolite with a SiO₂/Al₂O₃ ratio of 50 or less,further preferably 25 or less, a higher conversion of methanol and/ordimethyl ether can be achieved, and the production amount of methane asby-products can be more sufficiently reduced, and a higher selectivityof propane and butane can be achieved.

(Process for Producing a Catalyst According to the Present Invention)

A catalyst for producing a liquefied petroleum gas according to thisinvention is preferably produced by separately preparing a Pd- and/orPt-based catalyst component and a USY-type zeolite, and then mixingthem. By separately preparing a Pd- and/or Pt-based catalyst componentand a USY-type zeolite, a composition, a structure and a property ofeach component can be easily optimized for each function.

A Pd- and/or Pt-based catalyst component, in which Pd and/or Pt issupported on a support (e.g. silica), can be prepared by a known methodsuch as an impregnation method and a precipitation method.

A USY-type zeolite can be prepared by a known method, and a commerciallyavailable product can be used.

Some of Pd- and/or Pt-based catalyst components must be activated byreduction treatment before use, including those containing Pd and/or Ptas an oxide, nitrate or chloride. In this invention, it is notnecessarily required to activate a Pd- and/or Pt-based catalystcomponent by reduction treatment in advance. The Pd- and/or Pt-basedcatalyst component can be activated by reduction treatment of thecatalyst for producing a liquefied petroleum gas of this invention,before the beginning of the reaction, after producing the catalyst bymixing a Pd- and/or Pt-based catalyst component and a USY-type zeolite,and then molding the mixture.

The conditions of the reduction treatment can be determined, dependingon some factors such as the type of the Pd- and/or Pt-based catalystcomponent, as appropriate.

A catalyst for producing a liquefied petroleum gas according to thepresent invention can be produced by homogeneously mixing a Pd- and/orPt-based catalyst component and a USY-type zeolite, and then, ifnecessary, molding the mixture. A procedure of mixing and molding thesecatalyst components is not particularly limited, but is preferably a drymethod. When mixing and molding these catalyst components by a wetmethod, there may occur a compound transfer between these catalystcomponents, for example, neutralization due to transfer of a basiccomponent in a Pd- and/or Pt-based catalyst component to an acidic sitein a USY-type zeolite, leading to the change of a property optimized foreach function of these catalyst components, and the like. A catalyst canbe molded by an appropriate method such as an extrusion molding and atablet-compression molding.

In this invention, a Pd- and/or Pt-based catalyst component and aUSY-type zeolite to be mixed preferably have an average particle size of0.1 μm or more and 5 μm or less. Average particle sizes of a Pd- and/orPt-based catalyst component and a USY-type zeolite to be mixed are morepreferably 0.5 μm or more and 2 μm or less. By mixing a Pd- and/orPt-based catalyst component and a USY-type zeolite having an averageparticle size within the above range, a higher conversion of methanoland/or dimethyl ether can be achieved, and a higher selectivity ofpropane and butane can be achieved.

It is preferable that a Pd- and/or Pt-based catalyst component and aUSY-type zeolite to be mixed have the same average particle size.

2. Process for Producing a Liquefied Petroleum Gas

Next, there will be described a process for producing a liquefiedpetroleum gas comprising propane or butane, preferably propane, as amain component, by reacting at least one selected from the groupconsisting of methanol and dimethyl ether with hydrogen using at leastone of the catalysts as described above.

In the process for producing LPG according to this invention, a reactionraw material may be methanol or dimethyl ether alone, or may be amixture of methanol and dimethyl ether. When using a mixture of methanoland dimethyl ether as a reaction raw material, a ratio of methanol todimethyl ether is not particularly limited, and can be appropriatelydetermined.

The reaction can be conducted in a fixed bed, a fluidized bed or amoving bed. The reaction conditions such as a composition of a startinggas, a reaction temperature, a reaction pressure and a contact time witha catalyst can be appropriately determined. For example, the LPGproduction reaction may be carried out under the following conditions.

In the light of achieving a higher catalytic activity, a reactiontemperature is preferably 350° C. or higher, more preferably 360° C. orhigher, particularly preferably 400° C. or higher. In the light ofachieving a higher selectivity for a hydrocarbon and a higherselectivity for propane and butane, as well as a long catalyst life, areaction temperature is preferably 470° C. or lower, more preferably450° C. or lower.

In the light of achieving a higher activity and good operability of anapparatus, a reaction pressure is preferably 0.3 MPa or higher, morepreferably 0.4 MPa or higher. Furthermore, when a reaction pressure is0.8 MPa or higher, more preferably 1 MPa or higher, a higher selectivityfor propane and butane can be achieved. In the light of economicalefficiency and safety, a reaction pressure is preferably 3 MPa or lower,more preferably 2.5 MPa or lower.

A gas space velocity is preferably 1500 hr⁻¹ or more, more preferably1800 hr⁻¹ or more, in the light of economical efficiency. In addition, agas space velocity is preferably 10000 hr⁻¹ or less, more preferably5000 hr⁻¹ or less, in the light of achieving a higher activity and ahigher selectivity for propane and butane.

When a reaction raw material is methanol, a concentration of methanol ina gas fed into a reactor (also referred to as a “starting gas”) ispreferably 20 mol % or more, more preferably 30 mol % or more, in thelight of productivity and economical efficiency. In the light ofreducing a calorific value and a deterioration of a catalyst, aconcentration of methanol in a gas fed into a reactor is preferably 60mol % or less, more preferably 40 mol % or less.

When a reaction raw material is methanol, a concentration of hydrogen ina gas fed into a reactor is preferably 1 mole or more, more preferably1.2 moles or more per 1 mole of methanol, in the light of improving ahydrogenation rate and reducing deterioration of a catalyst. In thelight of productivity and economical efficiency, a concentration ofhydrogen in a gas fed into a reactor is preferably 3 moles or less, morepreferably 2 moles or less per 1 mole of methanol.

When a reaction raw material is dimethyl ether, a concentration ofdimethyl ether in a gas fed into a reactor is preferably 10 mol % ormore, more preferably 20 mol % or more, in the light of productivity andeconomical efficiency. In the light of reducing a calorific value and adeterioration of a catalyst, a concentration of dimethyl ether in a gasfed into a reactor is preferably 40 mol % or less, more preferably 30mol % or less.

When a reaction raw material is dimethyl ether, a concentration ofhydrogen in a gas fed into a reactor is preferably 2 mole or more, morepreferably 2.5 moles or more per 1 mole of dimethyl ether, in the lightof improving a hydrogenation rate and reducing deterioration of acatalyst. In the light of productivity and economical efficiency, aconcentration of hydrogen in a gas fed into a reactor is preferably 5moles or less, more preferably 4 moles or less per 1 mole of dimethylether.

When a reaction raw material is a mixture of methanol and dimethylether, concentrations of methanol, dimethyl ether and hydrogen in a gasfed into a reactor are preferably within the same range as the abovepreferable range when a reaction raw material is methanol and the abovepreferable range when a reaction raw material is dimethyl ether. And,these preferable ranges can be calculated based on a ratio of methanolto dimethyl ether.

A gas fed into a reactor may contain water, an inert gas and the like,in addition to at least one of methanol and dimethyl ether, which arereaction raw materials, and hydrogen. The gas fed into a reactor maycontain carbon monoxide and/or carbon dioxide.

At least one of methanol and dimethyl ether, and hydrogen may be mixed,and then fed into a reactor or, alternatively, these may be fed into areactor separately.

A starting gas can be dividedly fed into the reactor so as to control areaction temperature.

The reaction can be conducted in a fixed bed, a fluidized bed, a movingbed or the like, and can be preferably selected, taking both of controlof a reaction temperature and a regeneration method of the catalyst intoaccount. For example, a fixed bed may include a quench type reactor suchas an internal multistage quench type, a multitubular type reactor, amultistage type reactor having a plurality of internal heat exchangersor the like, a multistage cooling radial flow type, a double pipe heatexchange type, an internal cooling coil type, a mixed flow type, andother types of reactors.

When used, a catalyst for producing a liquefied petroleum gas can bediluted with silica, alumina or an inert and stable heat conductor forcontrolling a temperature. In addition, when used, a catalyst forproducing a liquefied petroleum gas can be applied to the surface of aheat exchanger for controlling a temperature.

According to the present invention, an LPG production reaction can becarried out with a conversion of methanol and/or dimethyl ether of 99%or more, particularly about 100%. Furthermore, according to the presentinvention, an LPG production reaction can be carried out with such ahigh activity and selectivity that a conversion of methanol and/ordimethyl ether to a hydrocarbon is 90% or more, particularly 95% ormore.

A reaction product gas thus produced (a lower-paraffin-containing gas)comprises a hydrocarbon containing propane or butane as a maincomponent. In the light of liquefaction properties, it is preferablethat the total content of propane and butane is higher in alower-paraffin-containing gas. According to this invention, there can beobtained a lower-paraffin-containing gas having a total content ofpropane and butane of 55% or more, preferably 60% or more on the basisof carbon to the hydrocarbon contained therein.

Furthermore, a lower-paraffin-containing gas produced preferablycontains more propane in comparison with butane, in the light ofinflammability and vapor pressure properties.

A lower-paraffin-containing gas produced generally comprises water; alow-boiling component having a lower boiling point or a lowersublimation point than the boiling point of propane; and a high-boilingcomponent having a higher boiling point than the boiling point ofbutane. Examples of a low-boiling component include hydrogen, which isan unreacted starting material; and ethane, methane, carbon monoxide andcarbon dioxide, which are by-products. Examples of a high-boilingcomponent include high-boiling paraffins (e.g. pentane, hexane and thelike), which are by-products.

Thus, water, a low-boiling component and a high-boiling component are,as necessary, separated from a lower-paraffin-containing gas produced,so as to obtain a liquefied petroleum gas (LPG) comprising propane orbutane as a main component. If necessary, methanol and/or dimethylether, which are unreacted starting materials, are also separated from alower-paraffin-containing gas by a known method.

Separation of water, a low-boiling component or a high-boiling componentcan be conducted in accordance with a known method.

Water can be separated by, for example, liquid-liquid separation.

A low-boiling component can be separated by, for example, gas-liquidseparation, absorption separation or distillation; more specifically,gas-liquid separation at an ambient temperature under increasedpressure, absorption separation at an ambient temperature underincreased pressure, gas-liquid separation with cooling, absorptionseparation with cooling, or combination thereof. Alternatively, for thispurpose, membrane separation or adsorption separation can be conducted,or these in combination with gas-liquid separation, absorptionseparation or distillation can be conducted. A gas recovery processcommonly employed in an oil factory (described in “Oil RefiningProcesses”, ed. The Japan Petroleum Institute, Kodansha Scientific,1998, pp. 28-32) can be applied to separation of a low-boilingcomponent.

A preferable method of separation of a low-boiling component is anabsorption process where a liquefied petroleum gas comprising propane orbutane as a main component is absorbed into an absorbent liquid such asa high-boiling paraffin gas having a higher boiling point than butane,and a gasoline.

A high-boiling component can be separated by, for example, gas-liquidseparation, absorption separation or distillation.

The conditions of separation may be determined as appropriate inaccordance with a known method.

If necessary, the gas may be pressurized and/or cooled so as to obtain aliquefied petroleum gas.

For consumer use, it is preferable that a content of a low-boilingcomponent in the LPG is reduced to 5 mol % or less (including 0 mol %)by separation, for example, in the light of safety in use.

The total content of propane and butane in the LPG thus produced may be90% or more, more preferably 95% or more (including 100%) on the basisof carbon. And a content of propane in the LPG produced may be 50% ormore, more preferably 60% or more, particularly preferably 65% or more(including 100%) on the basis of carbon. Thus, according to thisinvention, LPG having a composition suitable for a propane gas, which iswidely used as a fuel for household and business use, can be produced.

Next, there will be described an embodiment of a process for producingLPG according to this invention with reference to the drawing.

FIG. 1 shows an embodiment of an LPG production apparatus suitable forcarrying out a production process for LPG according to this invention.

First, methanol and/or dimethyl ether, which are reaction raw materials,and hydrogen are fed into a reactor 11 via a line 12. In the reactor 11,there is a catalyst layer 11 a comprising a catalyst for producing aliquefied petroleum gas according to this invention. In the reactor 11,a hydrocarbon gas containing propane or butane as a main component (alower paraffin-containing gas) is produced from methanol and/or dimethylether and hydrogen in the presence of the catalyst for producing aliquefied petroleum gas.

The hydrocarbon gas thus produced is pressurized and cooled, afteroptional removal of water or the like, and LPG, which is a product, isobtained from a line 13. Optionally, hydrogen and the like may beremoved from the LPG by, for example, gas-liquid separation.

The LPG production apparatus may be, as necessary, provided with abooster, a heat exchanger, a valve, an instrumentation controller and soon, which are not shown.

Thus, according to this invention, LPG is produced from at least one ofmethanol and dimethyl ether.

3. Process for Producing a Liquefied Petroleum Gas from aCarbon-Containing Starting Material

At present, methanol and dimethyl ether, which are used as a startingmaterial in this invention, are produced in an industrial scale.

Methanol is produced, for example, as follows.

First, a synthesis gas is produced by reacting a natural gas (methane)with at least one selected from the group consisting of H₂O, O₂ and CO₂in the presence of a reforming catalyst such as an Ni-based catalyst, ifnecessary, after removing a catalyst poisoning component such as sulfurand a sulfur compound from a natural gas (devulcanization and the like).A water-vapor reforming method, a complex reforming method and anautothermal reforming method of a natural gas (methane) are well knownas a process for producing a synthesis gas.

And, a synthesis gas may be also produced by reacting acarbon-containing starting material other than a natural gas with atleast one selected from the group consisting of H₂O, O₂ and CO₂, inaccordance with a known method. Any carbon-containing substance whichcan react with at least one selected from the group consisting of H₂O,O₂ and CO₂ to form H₂ and CO, can be used as a carbon-containingstarting material. For example, a lower hydrocarbon such as ethane,naphtha, a coal, and the like can be used as a carbon-containingstarting material.

Next, methanol is produced from the synthesis gas by reacting carbonmonoxide with hydrogen in the presence of a methanol synthesis catalyst.When using a Cu—Zn-based catalyst (a composite oxide containing Cu andZn) such as a Cu—Zn—Al composite oxide and a Cu—Zn—Cr composite oxide asa methanol synthesis catalyst, the reaction is generally carried out ata reaction temperature of about 230 to 300° C. and under a reactionpressure of about 2 to 10 MPa. When using a Zn—Cr-based catalyst (acomposite oxide containing Zn and Cr) as a methanol synthesis catalyst,the reaction is generally carried out at a reaction temperature of about250 to 400° C. and under a reaction pressure of about 10 to 60 MPa.

A product thus produced (crude methanol) generally comprises water;carbon monoxide, which is an unreacted starting material; carbon dioxideand dimethyl ether, which are by-products; and the like. In thisinvention, the crude methanol can be used as a starting material.

Dimethyl ether is produced by, for example, dehydration reaction ofmethanol using a solid acid catalyst such as aluminum phosphate.

A process for producing dimethyl ether from a synthesis gas directly,not via methanol, is being put to practical use. In the process,dimethyl ether can be produced by reacting carbon monoxide with hydrogenat a reaction temperature of about 230 to 280° C. and under a reactionpressure of about 3 to 7 MPa in the presence of a mixed catalyst of amethanol synthesis catalyst and a methanol dehydration catalyst, forexample, a mixed catalyst comprising a methanol synthesis catalyst and amethanol dehydration catalyst in a ratio of the methanol synthesiscatalyst:the methanol dehydration catalyst=1:2 to 2:1 (by weight), usinga slurry phase reactor.

A product thus produced (crude dimethyl ether) generally compriseswater; carbon monoxide, which is an unreacted starting material; carbondioxide and methanol, which are by-products; and the like. In thisinvention, the crude dimethyl ether can be used as a starting material.

According to this invention, a liquefied petroleum gas can be producedby producing a synthesis gas from a carbon-containing starting materialand at least one selected from the group consisting of H₂O, O₂ and CO₂(synthesis gas production step); feeding the obtained synthesis gas to acatalyst layer comprising a methanol synthesis catalyst, to produce areactant gas containing methanol and hydrogen (methanol productionstep); and feeding the reactant gas produced in the methanol productionstep to a catalyst layer comprising a catalyst for producing a liquefiedpetroleum gas, to produce a liquefied petroleum gas containing propaneor butane as a main component in accordance with the above process(liquefied petroleum gas production step).

Moreover, according to this invention, a liquefied petroleum gas can beproduced by producing a synthesis gas from a carbon-containing startingmaterial and at least one selected from the group consisting of H₂O, O₂and CO₂ (synthesis gas production step); feeding the obtained synthesisgas to a catalyst layer comprising a methanol synthesis catalyst and amethanol dehydration catalyst, to produce a reactant gas containingdimethyl ether and hydrogen (dimethyl ether production step); andfeeding the reactant gas produced in the dimethyl ether production stepto a catalyst layer comprising a catalyst for producing a liquefiedpetroleum gas, to produce a liquefied petroleum gas containing propaneor butane as a main component in accordance with the above process(liquefied petroleum gas production step).

A synthesis gas can be produced in accordance with a known methodincluding the method described above. Methanol and dimethyl ether can bealso produced in accordance with a known method including the methoddescribed above.

In the above process for producing LPG, a shift reactor may be placeddownstream of a reformer, which is a reactor for producing a synthesisgas, so that a synthesis gas composition can be adjusted by a shiftreaction (CO+H₂O→CO₂+H₂).

In the above process for producing LPG, a low-boiling componentseparated from the lower-paraffin-containing gas in the liquefiedpetroleum gas production step can be recycled as a starting material forthe synthesis gas production step.

The whole low-boiling components separated from thelower-paraffin-containing gas can be recycled to the synthesis gasproduction step. Alternatively, part of the low-boiling components maybe removed outside the system, while the rest of low-boiling componentsmay be recycled to the synthesis gas production step. Low-boilingcomponents can be recycled to the synthesis gas production step afterseparating only desired components.

In this case, in the synthesis gas production step, a content of alow-boiling component in a gas fed into a reformer, which is a reactor;in other words, a content of a recycled material may be determined asappropriate.

For the purpose of recycling a low-boiling component, a known technique,e.g. appropriately providing a recycle line with a pressurization meanscan be employed.

According to this invention, a liquefied petroleum gas can be producedfrom a synthesis gas or a carbon-containing starting material such as anatural gas by utilizing an existing methanol production plant or anexisting dimethyl ether production plant, and establishing an LPGproduction apparatus of this invention therewith.

EXAMPLES

The following will describe the present invention in more detail withreference to Examples. However, the present invention is not limited tothese Examples.

Example 1 Preparation of a Catalyst

A mechanically powdered catalyst in which 0.5 wt % of Pd was supportedon silica (Pd/SiO₂; average particle size: 1 μm) was used as a Pd-and/or Pt-based catalyst component. The catalyst was prepared asfollows.

The silica, which is a support for the Pd- and/or Pt-based catalystcomponent, was CARiACT G3 (trade name), produced by Fuji SilysiaChemical Ltd. The silica had a specific surface area of 820 m²/g, asdetermined by a BET method with N₂ as an adsorption gas, using ASAP2010(Shimadzu Corporation).

First, the silica was pulverized to 20 to 40 mesh, sized and dried. Andthen, 8.8 mL of a 50 mg/mL aqueous solution of Pd(NO₃)₂(NH₃)₂ was addeddrop by drop to 20 g of the silica. After sufficiently impregnating thesolution into pores, the silica was dried in a drying machine at 120° C.for 12 hours. The above process of impregnation and drying was repeatedtwo more times.

Then, the silica impregnated with Pd was calcined at 450° C. in the airfor 8 hours. Subsequently, it was mechanically pulverized to give a Pd-and/or Pt-based catalyst component.

A mechanically powdered proton-type USY zeolite with a SiO₂/Al₂O₃ ratioof 10, produced by Catalysts & Chemicals Industries Co., Ltd., (USY(10);average particle size: 1 μm) was used as a USY-type zeolite.

The Pd- and/or Pt-based catalyst component thus prepared and theUSY-type zeolite were homogeneously mixed with Pd/SiO₂:USY=1:2 (byweight). And, the mixture was molded by a tablet-compression and sizedto give a granular molded catalyst having an average particle size of 1mm.

(Production of LPG)

In a tubular reactor with an inner diameter of 6 mm was placed 1 g ofthe catalyst prepared as described above, and the catalyst was reducedunder a hydrogen stream at 400° C. for 2 hours before the beginning ofthe reaction.

After reduction treatment of the catalyst, a starting gas consisting of75 mol % of hydrogen and 25 mol % of dimethyl ether (H₂/DME=3 (molarratio)) was passed through the catalyst layer at a reaction temperatureof 375° C., a reaction pressure of 2.1 MPa and a gas space velocity of2000 hr⁻¹ (W/F=9.0 g·h/mol) to carry out the LPG production reaction.

Gas chromatographic analysis of the product indicated that, after threehours from the beginning of the reaction, a conversion of dimethyl etherwas 100%, a conversion of dimethyl ether to carbon monoxide was 4.3%, aconversion of dimethyl ether to carbon dioxide was 0.0%, and aconversion of dimethyl ether to a hydrocarbon was 95.6%. The producedhydrocarbon gas contained propane and butane in 60.4% on the basis ofcarbon. A conversion of dimethyl ether to propane and butane was 57.7%on the basis of carbon.

The results are shown in Table 1.

Example 2 Preparation of a Catalyst

A catalyst was prepared in the same way as Example 1, except that aproton-type USY zeolite with a SiO₂/Al₂O₃ ratio of 20 (USY(20)) was usedas a USY-type zeolite.

(Production of LPG)

Using the prepared catalyst, the LPG production reaction was carried outin the same way as Example 1.

Gas chromatographic analysis of the product indicated that, after threehours from the beginning of the reaction, a conversion of dimethyl etherwas 100%, a conversion of dimethyl ether to carbon monoxide was 2.7%, aconversion of dimethyl ether to carbon dioxide was 0.0%, and aconversion of dimethyl ether to a hydrocarbon was 97.3%. The producedhydrocarbon gas contained propane and butane in 65.2% on the basis ofcarbon. A conversion of dimethyl ether to propane and butane was 63.4%on the basis of carbon.

The results are shown in Table 1.

Example 3 Preparation of a Catalyst

A catalyst was prepared in the same way as Example 1, except that aproton-type USY zeolite with a SiO₂/Al₂O₃ ratio of 30 (USY(30)) was usedas a USY-type zeolite.

(Production of LPG)

Using the prepared catalyst, the LPG production reaction was carried outin the same way as Example 1.

Gas chromatographic analysis of the product indicated that, after threehours from the beginning of the reaction, a conversion of dimethyl etherwas 99.8%, a conversion of dimethyl ether to carbon monoxide was 2.7%, aconversion of dimethyl ether to carbon dioxide was 0.0%, and aconversion of dimethyl ether to a hydrocarbon was 97.1%. The producedhydrocarbon gas contained propane and butane in 64.3% on the basis ofcarbon. A conversion of dimethyl ether to propane and butane was 62.4%on the basis of carbon.

The results are shown in Table 1.

TABLE 1 Example 1 Example 2 Example 3 Catalyst Pd/SiO₂:USY(10) =Pd/SiO₂:USY(20) = Pd/SiO₂:USY(30) = 1:2 1:2 1:2 DME conversion (%) 100.0100.0 99.8 CO yield (%) 4.3 2.7 2.7 CO₂ yield (%) 0.0 0.0 0.0Hydrocarbon yield (%) 95.6 97.3 97.1 Product composition (%) C1(methane) 2.0 3.2 4.5 C2 (ethane) 15.4 12.2 11.1 C3 (propane) 25.4 25.624.5 C4 (butane) 35.0 39.5 39.8 C5 (pentane) 15.1 12.8 12.9 C6 (hexane)7.2 6.6 7.0 C3 + C4 60.4 65.2 64.3 C3 + C4 yield (%) 57.7 63.4 62.4

Example 4 Preparation of a Catalyst

A catalyst was prepared in the same way as Example 2, except that thePd/SiO₂ and the USY-type zeolite were homogeneously mixed withPd/SiO₂:USY(20)=1:1 (by weight).

(Production of LPG)

Using the prepared catalyst, the LPG production reaction was carried outin the same way as Example 1.

Gas chromatographic analysis of the product indicated that, after threehours from the beginning of the reaction, a conversion of dimethyl etherwas 99.8%, a conversion of dimethyl ether to carbon monoxide was 3.0%, aconversion of dimethyl ether to carbon dioxide was 0.0%, and aconversion of dimethyl ether to a hydrocarbon was 96.9%. The producedhydrocarbon gas contained propane and butane in 61.5% on the basis ofcarbon. A conversion of dimethyl ether to propane and butane was 59.6%on the basis of carbon.

The results are shown in Table 2. For comparison, the results of Example2 are also shown in Table 2.

TABLE 2 Example 2 Example 4 Catalyst Pd/SiO₂:USY(20) = Pd/SiO₂:USY(20) =1:2 1:1 DME conversion (%) 100.0 99.8 CO yield (%) 2.7 3.0 CO₂ yield (%)0.0 0.0 Hydrocarbon yield (%) 97.3 96.9 Product composition (%) C1(methane) 3.2 1.7 C2 (ethane) 12.2 15.0 C3 (propane) 25.6 25.4 C4(butane) 39.5 36.1 C5 (pentane) 12.8 15.1 C6 (hexane) 6.6 6.7 C3 + C465.2 61.5 C3 + C4 yield (%) 63.4 59.6

Example 5 Preparation of a Catalyst

A catalyst was prepared in the same way as Example 4, except thatCARiACT Q6 (trade name), produced by Fuji Silysia Chemical Ltd., wasused as a silica, which is a support for a Pd- and/or Pt-based catalystcomponent. The silica had a specific surface area of 450 m²/g, asdetermined by a BET method with N₂ as an adsorption gas, using ASAP2010(Shimadzu Corporation).

(Production of LPG)

Using the prepared catalyst, the LPG production reaction was carried outin the same way as Example 1.

Gas chromatographic analysis of the product indicated that, after threehours from the beginning of the reaction, a conversion of dimethyl etherwas 99.4%, a conversion of dimethyl ether to carbon monoxide was 1.2%, aconversion of dimethyl ether to carbon dioxide was 0.1%, and aconversion of dimethyl ether to a hydrocarbon was 98.2%. The producedhydrocarbon gas contained propane and butane in 66.0% on the basis ofcarbon. A conversion of dimethyl ether to propane and butane was 64.8%on the basis of carbon.

The results are shown in Table 3.

Example 6 Preparation of a Catalyst

A catalyst was prepared in the same way as Example 5, except that thePd/SiO₂ having an average particle size of 1 mm and the USY-type zeolite(USY(20)) having an average particle size of 1 mm were homogeneouslymixed.

(Production of LPG)

Using the prepared catalyst, the LPG production reaction was carried outin the same way as Example 1.

Gas chromatographic analysis of the product indicated that, after threehours from the beginning of the reaction, a conversion of dimethyl etherwas 97.3%, a conversion of dimethyl ether to carbon monoxide was 2.4%, aconversion of dimethyl ether to carbon dioxide was 0.1%, and aconversion of dimethyl ether to a hydrocarbon was 94.7%. The producedhydrocarbon gas contained propane and butane in 53.4% on the basis ofcarbon. A conversion of dimethyl ether to propane and butane was 50.6%on the basis of carbon.

The results are shown in Table 3.

TABLE 3 Example 5 Example 6 Catalyst Pd/SiO₂:USY(20) = Pd/SiO₂:USY(20) =1:1 1:1 Average particle size of 1 μm 1 mm a catalyst component DMEconversion (%) 99.4 97.3 CO yield (%) 1.2 2.4 CO₂ yield (%) 0.1 0.1Hydrocarbon yield (%) 98.2 94.7 Product composition (%) C1 (methane) 3.22.3 C2 (ethane) 12.7 14.5 C3 (propane) 25.6 21.1 C4 (butane) 40.4 32.3C5 (pentane) 12.9 16.2 C6 (hexane) 5.2 13.6 C3 + C4 66.0 53.4 C3 + C4yield (%) 64.8 50.6

Comparative Example 1 Preparation of a Catalyst

A mechanically powdered Cu—Zn-based methanol synthesis catalyst, C79produced by Süd Chemie Japan, Inc., (also referred to as “Cu—Zn”) and amechanically powdered proton-type USY zeolite with a SiO₂/Al₂O₃ ratio of12.2, produced by Catalysts & Chemicals Industries Co., Ltd., (alsoreferred to as “USY”) were homogeneously mixed with Cu—Zn:USY=1:1 (byweight). And, the mixture was molded by a tablet-compression and sizedto give a granular catalyst for producing a liquefied petroleum gashaving an average particle size of 1 mm.

(Production of LPG)

Using the prepared catalyst, the LPG production reaction was carried outin the same way as Example 1, except that a reaction temperature was340° C.

Gas chromatographic analysis of the product indicated that, after threehours from the beginning of the reaction, a conversion of dimethyl etherwas 99.9%, a conversion of dimethyl ether to carbon monoxide was 15.0%,a conversion of dimethyl ether to carbon dioxide was 16.0%, and aconversion of dimethyl ether to a hydrocarbon was 68.9%. The producedhydrocarbon gas contained propane and butane in 75.5% on the basis ofcarbon. A conversion of dimethyl ether to propane and butane was 52.0%on the basis of carbon.

The results are shown in Table 4.

Comparative Example 2 Preparation of a Catalyst

A catalyst was prepared in the same way as Example 1, except that aproton-type ZSM-5 with a SiO₂/Al₂O₃ ratio of 40 was used instead of aUSY-type zeolite.

(Production of LPG)

Using the prepared catalyst, the LPG production reaction was carried outin the same way as Example 1.

Gas chromatographic analysis of the product indicated that, after threehours from the beginning of the reaction, a conversion of dimethyl etherwas 100%, a conversion of dimethyl ether to carbon monoxide was 8.7%, aconversion of dimethyl ether to carbon dioxide was 0.1%, and aconversion of dimethyl ether to a hydrocarbon was 91.1%. The producedhydrocarbon gas contained propane and butane in 52.0% on the basis ofcarbon. A conversion of dimethyl ether to propane and butane was 47.4%on the basis of carbon.

The results are shown in Table 4.

Comparative Example 3 Preparation of a Catalyst

A 0.5 wt % Pd-supported proton-type ZSM-5 with a SiO₂/Al₂O₃ ratio of 40,produced by Tosoh Corporation, was used as a catalyst. The catalyst wasprepared as follows.

First, 0.0825 g of palladium chloride (purity: >99 wt %) was dissolvedin 10 mL of a 12.5 wt % aqueous ammonia solution at 40 to 50° C. Andthen, 150 mL of ion-exchanged water was added to the resulting solutionto obtain a Pd-containing solution. 10 g of ZSM-5 zeolite was added tothe obtained Pd-containing solution, and the mixture was heated andstirred at 60 to 70° C. for 6 hours. After the ion-exchange process, theresulting material was repeatedly filtrated and washed withion-exchanged water until no chloride ions were observed in a filtrate.

Then, the Pd ion-exchanged ZSM-5 was dried at 120° C. for 12 hours, andcalcined at 500° C. in an air for 2 hours. Subsequently, it wasmechanically pulverized, and then molded by a tablet-compression andsized to give a granular catalyst for producing a liquefied petroleumgas (Pd-ZSM-5) having an average particle size of 1 mm.

(Production of LPG)

Using the prepared catalyst, the LPG production reaction was carried outin the same way as Example 1, except that a reaction temperature was350° C.

Gas chromatographic analysis of the product indicated that, after threehours from the beginning of the reaction, a conversion of dimethyl etherwas 100%, a conversion of dimethyl ether to carbon monoxide was 1.4%, aconversion of dimethyl ether to carbon dioxide was 0.4%, and aconversion of dimethyl ether to a hydrocarbon was 98.2%. The producedhydrocarbon gas contained propane and butane in 50.6% on the basis ofcarbon. A conversion of dimethyl ether to propane and butane was 49.7%on the basis of carbon.

The results are shown in Table 4.

Comparative Example 4 Preparation of a Catalyst

A catalyst (Pd-USY(20); the amount of supported Pd: 0.5 wt %) wasprepared in the same way as Comparative Example 3, except that aproton-type USY zeolite with a SiO₂/Al₂O₃ ratio of 20 (USY(20)) was usedinstead of a proton-type ZSM-5.

(Production of LPG)

Using the prepared catalyst, the LPG production reaction was carried outin the same way as Example 1, except that a reaction temperature was350° C.

Gas chromatographic analysis of the product indicated that, after threehours from the beginning of the reaction, a conversion of dimethyl etherwas 89.5%, a conversion of dimethyl ether to carbon monoxide was 14.9%,a conversion of dimethyl ether to carbon dioxide was 0.2%, and aconversion of dimethyl ether to a hydrocarbon was 74.4%. The producedhydrocarbon gas contained propane and butane in 2.6% on the basis ofcarbon. A conversion of dimethyl ether to propane and butane was 1.9% onthe basis of carbon. The results are shown in Table 4.

TABLE 4 Comp. Comp. Comp. Comp. Exam. 1 Exam. 2 Exam. 3 Exam. 4 CatalystCu—Zn Pd/SiO₂ Pd-ZSM-5 Pd-USY(20) USY ZSM-5 DME conversion (%) 99.9100.0 100.0 89.5 CO yield (%) 15.0 8.7 1.4 14.9 CO₂ yield (%) 16.0 0.10.4 0.2 Hydrocarbon yield (%) 68.9 91.1 98.2 74.4 Product composition(%) C1 (methane) 4.4 14.3 1.8 94.9 C2 (ethane) 5.1 19.4 29.2 0.8 C3(propane) 19.7 38.2 33.4 2.0 C4 (butane) 55.8 13.8 17.3 0.6 C5 (pentane)10.9 7.0 11.3 0.3 C6 (hexane) 4.1 7.2 7.2 1.4 C3 + C4 75.5 52.0 50.6 2.6C3 + C4 yield (%) 52.0 47.4 49.7 1.9

INDUSTRIAL APPLICABILITY

As described above, a hydrocarbon containing propane or butane as a maincomponent, i.e. a liquefied petroleum gas (LPG), can be economicallyproduced with high activity, high selectivity and high yield from atleast one of methanol and dimethyl ether by using a catalyst forproducing a liquefied petroleum gas according to the present invention.

Furthermore, according to the present invention, a liquefied petroleumgas containing propane or butane as a main component can be economicallyproduced from a carbon-containing starting material such as a naturalgas, or from a synthesis gas.

1. A catalyst for producing a liquefied petroleum gas, which is used forproducing a liquefied petroleum gas containing propane or butane as amain component by reacting at least one selected from the groupconsisting of methanol and dimethyl ether with hydrogen, comprising aPd- and/or Pt-based catalyst component in which Pd and/or Pt issupported on a support; and a USY-type zeolite.
 2. A catalyst accordingto claim 1, wherein a ratio (by weight) of the Pd- and/or Pt-basedcatalyst component to the USY-type zeolite is 0.1 to 1.5 (Pd- and/orPt-based catalyst component/USY-type zeolite).
 3. A catalyst accordingto claim 1, wherein the amount of supported Pd and/or Pt in the Pd-and/or Pt-based catalyst component is 0.1 to 5% by weight.
 4. A catalystaccording to claim 1, wherein the support for the Pd- and/or Pt-basedcatalyst component is silica.
 5. A catalyst according to claim 4,wherein a specific surface area of the silica support for the Pd- and/orPt-based catalyst component is 450 m²/g or more.
 6. A catalyst accordingto claim 1, wherein the USY-type zeolite has a SiO₂/Al₂O₃ ratio of 5 to50.